JPH0127148B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for carburizing ferrous metals, particularly to a method in which nitrogen and ethanol are injected into the furnace, either separately or as a mixture, to create a furnace atmosphere. Equilibrium carbon concentration in the furnace atmosphere is determined by controlling the overall flow of feed components during the carburizing cycle and by controlling and/or adding water in the feed mixture and enrichment agents in the feed composition. Or it can be established and maintained by adding carburizing agents. Carburizing is a conventional method for case hardening ferrous metals, such as steel. In gas carburizing, steel is exposed to an atmosphere containing components that allow carbon to migrate to the surface of the metal and then diffuse into the body of the part. After the appropriate amount of carbon has been transferred, the steel is removed from the furnace and immediately quenched so that the carbon enriched areas become hard and wear resistant. Various furnace atmospheres are used for carburizing ferrous metals, but the following requirements must be met. First, it must not react with the steel to form oxides or other undesirable compounds.
This requirement excludes the presence of oxygen and more than small amounts of water or carbon dioxide. Secondly, they must contain substances that can act as carbon donors to the surface of the steel. Most commonly this is carbon monoxide, but sometimes hydrocarbons or oxygenated organic substances are used. Third, the atmosphere must activate the steel surface so that reaction with the carbon donor proceeds at an acceptable rate. At this time, hydrogen is very effective as an activator and is always present in the actual carburizing atmosphere.
Atmospheres derived from a variety of sources have been used, but the most commonly used are so-called endothermic gases produced by the partial combustion of natural gas in air. It is essentially 40% nitrogen and hydrogen
40% and carbon monoxide 20%. It is usually necessary to add small amounts of another component, usually natural gas, to increase the equilibrium carbon concentration. However, the use of an endothermic atmosphere is disadvantageous in the following respects. Expensive and sophisticated endothermic gas generators are required that require continuous maintenance and operator attention. Furthermore, the operation of the gas generator cannot be started or stopped at will. Once operational, it is necessary to continue operating even as atmospheric demands change from maximum to zero. Endothermic gas and the natural gas required to produce it are wasted during periods of low demand. Furthermore, natural gas is not uniform in composition and contains varying amounts of ethane, propane and higher hydrocarbons in addition to the main component methane. If the composition of the natural gas is not constant, the endothermic gas produced will vary substantially and create control problems. Finally, tapering the combustion and expensive natural gas to generate the atmosphere is inherently a waste of energy. Recent developments in creating the carburizing atmosphere include the use of inexpensive by-product nitrogen, which is introduced into the carburizing furnace along with the methanol. Methanol decomposes thermally to produce a mixture of hydrogen and carbon monoxide that serves as the carburizing atmosphere. It is usually necessary to add another component, often natural gas, to increase the equilibrium carbon concentration of such an atmosphere. However, methanol is typically produced from natural gas or oil, and as fossil fuels are becoming increasingly scarce and more expensive,
This measure again wastes valuable energy. Therefore, attempts have been made to use ethanol, which can be produced from renewable agricultural products, to generate a carburizing atmosphere. For example, US Pat. No. 2,673,821 describes creating a furnace atmosphere from a mixture of ethanol and water. Control of the equilibrium carbon concentration and prevention of large carbon deposits (soot formation) is achieved by adding water. however,
Blue-black surfaces on hardened pieces have been reported in the literature as a precursor to soot formation. Additionally, because no ingredients are used to create the atmosphere other than ethanol, which contains a relatively small amount of water, extra cost and waste is experienced. British Patent No. 816,051 vaguely describes a process in which nitrogen is saturated with volatile organic substances and passed through a heat treatment furnace to create an atmosphere suitable for carburizing. Although the details are unclear, it has been stated that ethanol can be used in this method. However, Traitement Thermique Volume 62 (1971)
Pages 35-45, published by Traitement Cermic (Paris, France), states that only methanol and acetone are suitable for this method. Ethanol has been reported to produce gum at the exit of the furnace and only weak and irregular carburization. As mentioned above, in the prior art, in order to adjust the equilibrium carbon concentration of the furnace, so-called endothermic gas generated by partial combustion of natural gas in the air,
The use of methanol, nitrogen, and ethanol has been proposed, but it has the following drawbacks. First, the use of endothermic gases requires expensive and sophisticated endothermic gas generators that require continuous maintenance and operator attention, and because the composition of natural gas is not constant, the endothermic gas produced varies substantially. Creates control problems. Additionally, the use of methanol and nitrogen requires the addition of another component, namely natural gas, to increase the equilibrium carbon concentration, as methanol thermally decomposes to produce a mixture of hydrogen and carbon monoxide, resulting in a resource shortage. cause problems. The use of ethanol also has the disadvantage of forming a gum at the exit of the furnace, resulting in weak and irregular carburization. The present invention has been made in view of the above-mentioned drawbacks of the prior art, and its purpose is to use a nitrogen-ethanol mixture containing a controlled amount of water together with carburizing gas to facilitate control of the furnace atmosphere and reduce operating costs. The objective is to reduce the amount of carbon dioxide and to effectively perform carburizing. That is, according to the present invention, 816°C (1500〓)
In carburizing a ferrous metal article with nitrogen and ethanol injected into a furnace containing the ferrous metal article to be carburized maintained at a temperature exceeding nitrogen,
Adjusting the total feed by adding water to give a 1:1 molar ratio of ethanol and water in the ethanol and water feed and furnace dimensions and configuration, furnace loading, composition of the article to be carburized, Adding an amount of enrichment agent effective to achieve the desired equilibrium carbon concentration as determined by the measured furnace temperature, desired depth of case, composition of the enrichment agent, and analysis of the furnace atmosphere during the carburizing cycle. A method of carburizing a ferrous metal article is provided comprising controlling the equilibrium carbon concentration of the furnace atmosphere. The method of the invention requires adding water such that the molar ratio of ethanol and water in the nitrogen, ethanol and water feed is 1:1;
At this time, if the ratio of ethanol to water exceeds 1:1, it must be avoided because it increases the working cost and may increase the generation of soot. Further, if the ratio is lower than 1:1, it must be avoided since it may lead to decarburization and/or oxidation of copper. Ferrous metal articles can be effectively carburized utilizing a mixture of nitrogen and ethanol introduced into a carburizing furnace either as separate streams or simultaneously as a mixture. An aspect of the invention is a method that utilizes a nitrogen-ethanol base mixture supplemented by controlled amounts of water and the addition of a hydrocarbon enrichment or carburizing agent. Controlling the equilibrium carbon concentration of the furnace atmosphere by controlling the feed composition and overall flow through the furnace is included. In embodiments of the present invention, a suitable base furnace atmosphere similar in composition to that derived from nitrogen and methanol is created by passing a stream of nitrogen doped with ethanol and water in a 1:1 molar ratio through the furnace. I can do it. At a furnace temperature of about 1500°C to about 1900°C (816°C to 1038°C), ethanol and water react to form carbon monoxide and hydrogen in a ratio of about 1:2, along with small amounts of methane, carbon dioxide, and water. The gas contained in the gas is generated. The obtained furnace atmosphere can be used for neutral hardening of low carbon steels. If carburization is desired, the equilibrium carbon concentration of the atmosphere can be substantially increased by enriched gases such as natural gas containing methane, propane, butane, ethane, and mixtures thereof. The equilibrium carbon concentration of the atmosphere is continuously measured by suitable means such as a wire sensor. Alternatively, the atmosphere may be continuously analyzed for carbon monoxide and carbon dioxide concentrations by gas chromatography or infrared analysis. Equilibrium carbon concentrations are calculated from these gas analysis values and can be adjusted upward or downward by varying the enrichment gas addition. Increasing the amount of enriched gas increases the equilibrium carbon concentration, while decreasing the flow of enriched gas decreases the equilibrium carbon concentration.
Control of enrichment gas flow may be performed manually or automatically using well-known and commonly available equipment. The following examples illustrate how to practice the invention. EXAMPLE 1 A 7.5 cubic foot batch furnace with a radiant tube heater and circulation fan is used to illustrate the generation of typical furnace atmospheres and how they can be effectively used to carburize steel parts. In a series of experiments, the furnace was operated without charge, but the propane addition was varied over a considerable range. Ethanol and water were separately sprayed as liquids into the furnace through a port that was also used to introduce gaseous nitrogen. Propane was introduced into the nitrogen stream before entering the furnace. Samples of the furnace atmosphere were taken continuously and analyzed frequently by gas chromatography. Thickness 0.005cm (0.002 inch)
The equilibrium carbon concentration was measured by suspending a steel slab in a furnace. At the end of the experiment, the specimens were quickly removed, cooled, and analyzed for carbon. The results are shown in the table. "Theoretical %C" in the table is the theoretical equilibrium carbon concentration calculated from the individual analysis values for carbon dioxide and carbon monoxide. "%C test piece" in the table is the actual analysis value of carbon in the sample. It is clear that the calculated and measured equilibrium carbon concentrations agree.

【table】

[Table] Abbreviations for eat.
Example 2 Using the furnace and procedure described in Example 1
Carburized 15 lbs of AISI type 1010 rivets.
The feed stream and furnace gas analysis values are shown in the table below.

【table】

[Table] Abbreviations indicating feet.
After 2.5 hours at a given temperature in each test, the rivet was removed from the oven, cooled, and subjected to metallographic examination to determine total case depth and effective case depth. The results of these measurements are shown in the table.

[Table] These results are completely satisfactory and the results obtained when test 2 was carried out at 1700 °C are comparable to those obtained at the same temperature using an atmosphere derived from methanol, nitrogen and natural gas. substantially the same. The basic gas generating components fed to the furnace are approximately 85% from approximately 0% nitrogen, approximately 50% ethanol and approximately 50% water.
It may range up to nitrogen, 7.5% ethanol and 7.5% water. A preferred maximum amount of nitrogen in the feed gas is about 80%, with the remainder being about 10% ethanol and about 10% water. Even if the nitrogen content is further increased, the carburization rate is low and insufficient. The minimum nitrogen content depends on the specific application. In some situations, a base gas derived entirely from ethanol and water is advantageous at the beginning of the carburization process by providing the highest and most uniform amount of carbon transfer. However, such atmospheres are expensive and it is desirable to begin dilution with nitrogen if high carbon transfer rates can no longer be maintained. An ethanol to water ratio of about 1:1 is preferred, although higher ratios can be used to obtain somewhat higher equilibrium carbon concentrations. Ratios significantly lower than 1:1 should be avoided as they may lead to decarburization and/or oxidation of the steel. The enrichment gas to ethanol ratio may vary from zero to a value that produces the desired equilibrium carbon concentration in the furnace. A general explanation for the upper limit cannot be given in detail because this upper limit depends on many factors, including not only the desired equilibrium carbon concentration but also the furnace temperature, the amount of gas circulation, and the surface area of the part to be carburized. The values described in Example 2 are typical of those that may be experienced when using propane as the enrichment gas. It is clear that materials containing lower carbon per molecule are required in larger quantities than propane. The temperature ranges from about 1500〓 (816℃) to about 1900〓 (about 1038℃)
It may be within the range. Water and ethanol can be introduced separately as liquids or vapors or in co-streams. Generally, the simplest operation involves mixing the liquid thoroughly and then pumping it as a liquid into the furnace via a spray nozzle or other suitable device that ensures rapid and safe vaporization and dispersion of the vapor throughout the furnace. obtained when supplied with The process according to the invention can be used in place of existing gas carburizing methods in batch furnaces and with appropriate furnace control in continuous furnaces. Existing furnaces can be easily adapted to the method of the present invention without the need to modify existing equilibrium carbon concentration measurement equipment.

Claims (1)

[Claims] 1. In carburizing a ferrous metal article with nitrogen and ethanol injected into a furnace containing the ferrous metal article to be carburized maintained at a temperature in excess of 816°C (1500°C), Adjust the total feed by adding water to give a 1:1 molar ratio of ethanol and water in the nitrogen, ethanol and water feeds and adjust the furnace dimensions and configuration, furnace loading, article to be carburized. Adding an amount of enrichment agent effective to achieve the desired equilibrium carbon concentration as determined by composition, measured furnace temperature, desired depth of case, composition of the enrichment agent, and analysis of the furnace atmosphere during the carburizing cycle. A method for carburizing a ferrous metal article, comprising controlling the equilibrium carbon concentration of the furnace atmosphere. 2 The furnace temperature is 1550〓(843℃) and 1900〓(1038℃).
2. A method according to claim 1, wherein the temperature is between 0.degree. 3. the feed is 7.5-50% ethanol by volume;
A method according to claim 1, consisting essentially of 7.5 to 50% water and the remainder up to 85% nitrogen. 4. The method of claim 3, wherein the feed consists essentially of 10% ethanol, 10% water and the balance nitrogen and enriched gas by volume. 5 The enriched gas is methane, propane, butane,
The method of claim 1, wherein the method is selected from the group consisting of natural gas substantially containing ethane and mixtures thereof.